A vehicle may be equipped with an electric power steering system. The electric power steering system uses an electric motor to assist the driver of the vehicle in turning the steering wheels of the vehicle. Sensors detect the position and torque of the steering column and/or steering wheel, as well as the current operating conditions of the vehicle, and a steering controller applies an assistive torque via the motor, to decrease the amount of torque that the driver must apply to turn the steering wheel, and thereby turn the steering wheels of the vehicle.
The amount of assistive torque that the steering controller controls the motor to apply varies with the operating conditions of the vehicle. The vehicle controller may reference a calibration table that relates various operating conditions of the vehicle to a desired assistive torque. The calibration table is stored in an electronic memory of the steering controller. The calibration table must be defined to provide a desirable amount of assistive torque for the various operating conditions of the vehicle. If the amount of assistive torque is too low, the steering wheel will require a higher level of torque from the driver to turn, which may be undesirable to some drivers. Alternatively, if the assistive torque is too high, the steering wheel may turn too freely, which may also be undesirable for some drivers. Defining the values for the assistive torque in the calibration table may be referred to as tuning the calibration table, and is typically done during vehicle development.
Electric power steering systems are difficult to model electronically. Accordingly, in the past, tuning the calibration table for electric power steering systems has been done by installing the electric power steering system on a prototype vehicle, test driving the prototype vehicle with a defined calibration table, and then adjusting the calibration table based on the subjective feel observed by the test driver of the prototype vehicle.